Optical construction and display system incorporating same

ABSTRACT

Optical constructions are disclosed. A disclosed optical construction includes a reflective polarizer layer, and an optical film that is disposed on the reflective polarizer layer. The optical film has an optical haze that is not less than about 50%. Substantial portions of each two neighboring major surfaces in the optical construction are in physical contact with each other. The optical construction has an axial luminance gain that is not less than about 1.2.

RELATED APPLICATIONS

This application is related to the following U.S. patent applicationswhich are incorporated by reference: U.S. Publication No. 2012/0038990;U.S. Publication No. 2015/0049384; U.S. Pat. No. 8,964,146; U.S. Pat.No. 8,891,038; U.S. Publication No. 2012/0021134; and U.S. Pat. No.8,808,811.

FIELD OF THE INVENTION

This invention generally relates to optical constructions that include areflective polarizer layer and an optical film that has a low index ofrefraction, or an optical film that exhibits somelow-refractive-index-like properties. The invention is furtherapplicable to display systems, such as liquid crystal display systems,incorporating such optical constructions.

BACKGROUND

Optical displays, such as liquid crystal displays (LCDs), are becomingincreasingly commonplace, finding use for example in many applicationsuch as mobile telephones, hand-held computer devices ranging frompersonal digital assistants (PDAs) to electronic games, to largerdevices such as laptop computers, LCD monitors and television screens.LCDs typically include one or more light management films to improveddisplay performance, such as output luminance, illumination uniformity,viewing angle, and overall system efficiency. Exemplary light managementfilms include prismatically structured films, reflective polarizers,absorbing polarizers, and diffuser films.

The light management films are typically stacked between a backlightassembly and a liquid crystal panel. From a manufacturing perspective,several issues can arise from the handling and assembly of severaldiscrete film pieces. These problems include, inter alia, the excesstime required to remove protective liners from individual optical films,along with the increased chance of damaging a film when removing theliner. In addition, the insertion of multiple individual sheets to thedisplay frame is time consuming and the stacking of individual filmsprovides further opportunity for the films to be damaged. All of theseproblems can contribute to diminished overall throughput or to reducedyield, which leads to higher system cost.

SUMMARY OF THE INVENTION

Generally, the present invention relates to optical constructions. Inone embodiment, an optical construction includes an optical diffuserlayer that has an optical haze that is not less than about 30%, anoptical film that is disposed on the optical diffuser layer and has anindex of refraction that is not greater than about 1.3 and an opticalhaze that is not greater than about 5%, and a reflective polarizer layerthat is disposed on the optical film. Substantial portions of each twoneighboring major surfaces in the optical construction are in physicalcontact with each other. In some cases, the optical film includes abinder, a plurality of interconnected voids, and a plurality ofparticles, where the weight ratio of the binder to the plurality of theparticles is not less than about 1:2. In some cases, the reflectivepolarizer layer can be a multilayer optical film that includesalternating layers, where at least one of the alternating layersincludes a birefringent material. In some cases, the reflectivepolarizer layer includes a wire grid reflective polarizer, or acholesteric reflective polarizer. In some cases, at least 50%, or atleast 70%, or at least 90%, of each two neighboring major surfaces inthe optical construction are in physical contact with each other. Insome cases, the optical construction has an axial luminance gain of noless than about 1.2, or no less than about 1.3, or no less than about1.4.

In another embodiment, an optical construction includes a reflectivepolarizer layer, and an optical film that is disposed on the reflectivepolarizer layer and has an optical haze that is not less than about 50%.Substantial portions of each two neighboring major surfaces in theoptical construction are in physical contact with each other. Theoptical construction has an axial luminance gain that is not less thanabout 1.2.

In another embodiment, an optical construction includes a reflectivepolarizer layer, and an optical film that is disposed on the reflectivepolarizer layer and has a plurality of voids and an optical haze that isnot less than about 50%. Substantial portions of each two neighboringmajor surfaces in the optical construction are in physical contact witheach other.

In another embodiment, an optical stack includes an absorbing polarizerlayer, an optical film comprising a plurality of voids, and a reflectivepolarizer layer. Substantial portions of each two neighboring majorsurfaces in the optical stack are in physical contact with each other.In some cases, the optical film is disposed between the absorbingpolarizer layer and the reflective polarizer layer. In some cases, theoptical film has an optical haze that is not less than about 50%. Insome cases, the optical film has an optical haze that is not greaterthan about 10%. In some cases, the optical stack further includes anoptical diffuser layer that has an optical haze that is not less thanabout 50%.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood and appreciated inconsideration of the following detailed description of variousembodiments of the invention in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic side-view of an optical construction;

FIG. 2 is a schematic side-view of another optical construction;

FIG. 3 is a schematic side-view of another optical construction;

FIG. 4A is a schematic side-view of a display system;

FIG. 4B is a schematic side-view of another display system;

FIG. 5A is a schematic side-view of another display system;

FIG. 5B is a schematic side-view of another display system;

FIG. 6 is an optical image of a porous optical film;

FIG. 7 is an optical image of another porous optical film;

FIG. 8 is an optical image of another porous optical film;

FIG. 9 is a schematic side-view of an optical system for measuringscattering properties of an optical diffuser;

FIG. 10 is the scattering distribution for a porous optically diffusivefilm and a non-porous optically diffusive film in air;

FIG. 11 is the scattering distribution for the two films in FIG. 10 in ahigh-index medium;

FIG. 12 is a schematic side-view of an optical construction;

FIG. 13 is a schematic side-view of another optical construction;

FIG. 14 is a schematic side-view of another optical construction;

FIG. 15 is a schematic side-view of another optical construction;

FIG. 16 is a schematic side-view of another optical construction;

FIG. 17 is a schematic side-view of a display system; and

FIG. 18 is a schematic side-view of another display system.

In the specification, a same reference numeral used in multiple figuresrefers to the same or similar elements having the same or similarproperties and functionalities.

DETAILED DESCRIPTION

This invention generally relates to optical constructions that include areflective polarizer and an optical film that includes a plurality ofvoids, such as a plurality of interconnected voids. In some cases, theoptical film has a low optical haze and a low effective index ofrefraction, such as an optical haze of less than about 5% and aneffective index of refraction that is less than about 1.3. In somecases, the optical film has a high optical haze and/or high diffuseoptical reflectance while exhibiting some low-refractive-index-likeoptical properties, such as, for example, the ability to support totalinternal reflection or enhance internal reflection.

The disclosed optical constructions can be incorporated into variousoptical or display systems such as, for example, a liquid crystaldisplay system, to improve system durability, reduce manufacturing andassembly cost, and reduce the overall thickness of the system whileimproving, maintaining or substantially maintaining at least some of thesystem optical properties such as, for example, the on-axis brightnessand contrast of an image displayed by the system.

The optical films disclosed herein include a plurality of voids, such asa plurality of interconnected voids or a network of voids, dispersed ina binder. The voids in the plurality of interconnected voids areconnected to one another via hollow tunnels or hollow tunnel-likepassages. The voids are not necessarily free of all matter and/orparticulates. For example, in some cases, a void may include one or moresmall fiber- or string-like objects that include, for example, a binderand/or nano-particles. Some disclosed optical films include multiplepluralities of interconnected voids or multiple networks of voids wherethe voids in each plurality or network are interconnected. In somecases, in addition to multiple pluralities of interconnected voids, thedisclosed optical films include a plurality of closed or unconnectedvoids meaning that the voids are not connected to other voids viatunnels.

Some disclosed optical films support total internal reflection (TIR) orenhanced internal reflection (EIR) by virtue of including a plurality ofvoids. When light that travels in an optically clear non-porous mediumis incident on a stratum possessing high porosity, the reflectivity ofthe incident light is much higher at oblique angles than at normalincidence. In the case of no or low haze voided films, the reflectivityat oblique angles greater than the critical angle is close to about100%. In such cases, the incident light undergoes total internalreflection (TIR). In the case of high haze voided films, the obliqueangle reflectivity can be close to 100% over a similar range of incidentangles even though the light may not undergo TIR. This enhancedreflectivity for high haze films is similar to TIR and is designated asEnhanced Internal Reflectivity (EIR). As used herein, by a porous orvoided optical film enhancing internal reflection (EIR), it is meantthat the reflectance at the boundary of the voided and non-voided strataof the film or film laminate is greater with the voids than without thevoids.

The voids in the disclosed optical films have an index of refractionn_(v) and a permittivity ∈_(v), where n_(v) ²=∈_(v), and the binder hasan index of refraction n_(b) and a permittivity ∈_(b), where n_(b)²=∈_(b). In general, the interaction of an optical film with light, suchas light that is incident on, or propagates in, the optical film,depends on a number of film characteristics such as, for example, thefilm thickness, the binder index, the void or pore index, the pore shapeand size, the spatial distribution of the pores, and the wavelength oflight. In some cases, light that is incident on or propagates within theoptical film, “sees” or “experiences” an effective permittivity ∈_(eff)and an effective index n_(eff), where n_(eff) can be expressed in termsof the void index n_(v), the binder index n_(b), and the film porosityor void volume fraction “f”. In such cases, the optical film issufficiently thick and the voids are sufficiently small so that lightcannot resolve the shape and features of a single or isolated void. Insuch cases, the size of at least a majority of the voids, such as atleast 60% or 70% or 80% or 90% of the voids, is not greater than aboutλ/5, or not greater than about λ/6, or not greater than about λ/8, ornot greater than about λ/10, or not greater than about λ/20, where λ isthe wavelength of light.

In some cases, light that is incident on a disclosed optical film is avisible light meaning that the wavelength of the light is in the visiblerange of the electromagnetic spectrum. In such cases, the visible lighthas a wavelength that is in a range from about 380 nm to about 750 nm,or from about 400 nm to about 700 nm, or from about 420 nm to about 680nm. In such cases, the optical film can reasonably be assigned aneffective index of refraction if the size of at least a majority of thevoids, such as at least 60% or 70% or 80% or 90% of the voids, is notgreater than about 70 nm, or not greater than about 60 nm, or notgreater than about 50 nm, or not greater than about 40 nm, or notgreater than about 30 nm, or not greater than about 20 nm, or notgreater than about 10 nm.

In some cases, the disclosed optical films are sufficiently thick sothat the optical film can reasonably have an effective index that can beexpressed in terms of the indices of refraction of the voids and thebinder, and the void or pore volume fraction or porosity. In such cases,the thickness of the optical film is not less than about 100 nm, or notless than about 200 nm, or not less than about 500 nm, or not less thanabout 700 nm, or not less than about 1000 nm.

When the voids in a disclosed optical film are sufficiently small andthe optical film is sufficiently thick, the optical film has aneffective permittivity ∈_(eff) that can be expressed as:

∈_(eff) =f∈ _(v)+(1−f)∈_(b)  (1)

In such cases, the effective index n_(eff) of the optical film can beexpressed as:

n _(eff) ² =fn _(v) ²+(1−f)n _(b) ²  (2)

In some cases, such as when the difference between the indices ofrefraction of the pores and the binder is sufficiently small, theeffective index of the optical film can be approximated by the followingexpression:

n _(eff) =fn _(v)+(1−f)n _(b)  (3)

In such cases, the effective index of the optical film is the volumeweighted average of the indices of refraction of the voids and thebinder. For example, an optical film that has a void volume fraction ofabout 50% and a binder that has an index of refraction of about 1.5, hasan effective index of about 1.25.

FIG. 1 is a schematic side-view of an optical construction 100 thatincludes a reflective polarizer layer 110 disposed on an optical film120 that includes a plurality of voids 130 having an index n_(v)dispersed in a binder 170 having an index n_(b). Reflective polarizerlayer 110 includes a top major surface 112 and a bottom major surface114. Optical film 120 includes a top major surface 122 and a bottommajor surface 124.

In some cases, the primary optical effect of voids 130 is to affect theeffective index and not to, for example, scatter light. In such cases,the optical haze of optical film 120 is not greater than about 5%, ornot greater than about 4%, or not greater than about 3.5%, or notgreater than about 4%, or not greater than about 3%, or not greater thanabout 2.5%, or not greater than about 2%, or not greater than about1.5%, or not greater than about 1%. In such cases, the effective indexof the optical film is not greater than about 1.35, or not greater thanabout 1.3, or not greater than about 1.25, or not greater than about1.2, or not greater than about 1.15, or not greater than about 1.1, ornot greater than about 1.05. In such cases, the thickness of opticalfilm 120 is not less than about 100 nm, or not less than about 200 nm,or not less than about 500 nm, or not less than about 700 nm, or notless than about 1,000 nm, or not less than about 1500 nm, or not lessthan about 2000 nm.

For light normally incident on optical film 120, optical haze, as usedherein, is defined as the ratio of the transmitted light that deviatesfrom the normal direction by more than 4 degrees to the totaltransmitted light. Haze values disclosed herein were measured using aHaze-guard Plus haze meter (BYK-Gardiner, Silver Springs, Md.) accordingto the procedure described in ASTM D1003.

In some cases, optical film 120 supports or promote total internalreflection (TIR) or enhance internal reflection meaning that thereflection is greater than what a material with index n_(b) wouldproduce. In such cases, optical film 120 is sufficiently thick so thatthe evanescent tail of a light ray that undergoes total internalreflection at a surface of the optical film, does not optically couple,or optically couples very little, across the thickness of the opticalfilm. In such cases, the thickness of optical film 120 is not less thanabout 1 micron, or not less than about 1.1 micron, or not less thanabout 1.2 microns, or not less than about 1.3 microns, or not less thanabout 1.4 microns, or not less than about 1.5 microns, or not less thanabout 1.7 microns, or not less than about 2 microns. A sufficientlythick optical film 120 can prevent or reduce an undesired opticalcoupling of the evanescent tail of an optical mode across the thicknessof the optical film.

In some cases, optical film 120 has a high optical haze. In such cases,the optical haze of the optical film is not less than about 40%, or notless than about 50%, or not less than about 60%, or not less than about70%, or not less than about 80%, or not less than about 90%, or not lessthan about 95%.

In some cases, optical film 120 has a high diffuse optical reflectance.In such cases, the diffuse optical reflectance of the optical film isnot less than about 30%, or not less than about 40%, or not less thanabout 50%, or not less than about 60%.

In some cases, optical film 120 has a high optical clarity. For lightnormally incident on optical film 120, optical clarity, as used herein,refers to the ratio (T₁−T₂)/(T₁+T₂), where T₁ is the transmitted lightthat deviates from the normal direction between 1.6 and 2 degrees, andT₂ is the transmitted light that lies between zero and 0.7 degrees fromthe normal direction. Clarity values disclosed herein were measuredusing a Haze-guard Plus haze meter from BYK-Gardiner. In the cases whereoptical film 120 has a high optical clarity, the clarity is not lessthan about 40%, or not less than about 50%, or not less than about 60%,or not less than about 70%, or not less than about 80%, or not less thanabout 90%, or not less than about 95%.

In some cases, optical film 120 has a low optical clarity. In suchcases, the optical clarity of the optical film is not greater than about10%, or not greater than about 7%, or not greater than about 5%, or notgreater than about 4%, or not greater than about 3%, or not greater thanabout 2%, or not greater than about 1%.

In general, optical film 120 can have any porosity or void volumefraction that may be desirable in an application. In some cases, thevolume fraction of plurality of voids 130 in optical film 120 is notless than about 20%, or not less than about 30%, or not less than about40%, or not less than about 50%, or not less than about 60%, or not lessthan about 70%, or not less than about 80%, or not less than about 90%.

In some cases, optical film 120 also includes a plurality of particles150 dispersed in binder 170. Particles 150 can have any size that may bedesirable in an application. For example, in some cases at least amajority of the particles, such as at least 60% or 70% or 80% or 90% or95% of the particles, have a size that is in a desired range. Forexample, in some cases, at least a majority of the particles, such as atleast 60% or 70% or 80% or 90% or 95% of the particles, have a size thatis not greater than about 5 microns, or not greater than about 3microns, or not greater than about 2 microns, or not greater than about1 micron, or not greater than about 700 nm, or not greater than about500 nm, or not greater than about 200 nm, or not greater than about 100nm, or not greater than about 50 nm.

In some cases, plurality of particles 150 has an average particle sizethat is not greater than about 5 microns, or not greater than about 3microns, or not greater than about 2 microns, or not greater than about1 micron, or not greater than about 700 nm, or not greater than about500 nm, or not greater than about 200 nm, or not greater than about 100nm, or not greater than about 50 nm.

In some cases, particles 150 are sufficiently small so that the primaryoptical effect of the particles is to affect the effective index ofoptical film 120. For example, in such cases, particles have an averagesize that is not greater than about λ/5, or not greater than about λ/6,or not greater than about λ/8, or not greater than about λ/10, or notgreater than about λ/20, where λ is the wavelength of light. As anotherexample, the average particle size is not greater than about 70 nm, ornot greater than about 60 nm, or not greater than about 50 nm, or notgreater than about 40 nm, or not greater than about 30 nm, or notgreater than about 20 nm, or not greater than about 10 nm.

Particles 150 can have any shape that may be desirable or available inan application. For example, particles 150 can have a regular orirregular shape. For example, particles 150 can be approximatelyspherical. As another example, the particles can be elongated. In suchcases, optical film 120 includes a plurality of elongated particles 150.In some cases, the elongated particles have an average aspect ratio thatis not less than about 1.5, or not less than about 2, or not less thanabout 2.5, or not less than about 3, or not less than about 3.5, or notless than about 4, or not less than about 4.5, or not less than about 5.In some cases, the particles can be in the form or shape of astring-of-pearls (such as Snowtex-PS particles available from NissanChemical, Houston, Tex.) or aggregated chains of spherical or amorphousparticles, such as fumed silica. Particles 150 can be any type particlesthat may be desirable in an application. For example, particles 150 canbe organic or inorganic particles. For example, particles 150 can besilica, zirconium oxide or alumina particles.

Particles 150 may or may not be functionalized. In some cases, particles150 are not functionalized. In some cases, particles 150 arefunctionalized so that they can be dispersed in a desired solvent orbinder 170 with no, or very little, clumping. In some cases, particles150 can be further functionalized to chemically bond to binder 170. Forexample, particles 150 can be surface modified and have reactivefunctionalities or groups to chemically bond to binder 170. In suchcases, at least a significant fraction of particles 150 is chemicallybound to the binder. In some cases, particles 150 do not have reactivefunctionalities to chemically bond to binder 170. In such cases,particles 150 can be physically bound to binder 170.

In some cases, some of the particles have reactive groups and others donot have reactive groups. For example in some cases, about 10% of theparticles have reactive groups and about 90% of the particles do nothave reactive groups, or about 15% of the particles have reactive groupsand about 85% of the particles do not have reactive groups, or about 20%of the particles have reactive groups and about 80% of the particles donot have reactive groups, or about 25% of the particles have reactivegroups and about 75% of the particles do not have reactive groups, orabout 30% of the particles have reactive groups and about 60% of theparticles do not have reactive groups, or about 35% of the particleshave reactive groups and about 65% of the particles do not have reactivegroups, or about 40% of the particles have reactive groups and about 60%of the particles do not have reactive groups, or about 45% of theparticles have reactive groups and about 55% of the particles do nothave reactive groups, or about 50% of the particles have reactive groupsand about 50% of the particles do not have reactive groups, or about 55%of the particles have reactive groups and about 45% of the particles donot have reactive groups, or about 60% of the particles have reactivegroups and about 40% of the particles do not have reactive groups, orabout 65% of the particles have reactive groups and about 35% of theparticles do not have reactive groups, or about 70% of the particleshave reactive groups and about 30% of the particles do not have reactivegroups, or about 75% of the particles have reactive groups and about 25%of the particles do not have reactive groups, or about 80% of theparticles have reactive groups and about 20% of the particles do nothave reactive groups, or about 85% of the particles have reactive groupsand about 15% of the particles do not have reactive groups, or about 90%of the particles have reactive groups and about 10% of the particles donot have reactive groups.

Binder 170 can be or include any material that may be desirable in anapplication. For example, binder 170 can be a UV curable material thatforms a polymer, such as a cross-linked polymer. In some cases, binder170 can be any polymerizable material, such as a polymerizable materialthat is radiation-curable.

In general, the weight ratio of binder 170 to plurality of particles 150can be any ratio that may be desirable in an application. In some cases,the weight ratio of the binder to the plurality of the particles is notless than about 1:1, or not less than about 1.5:1, or not less thanabout 2:1, or not less than about 2.5:1, or not less than about 3:1, ornot less than about 3.5:1, or not less than about 4:1.

In some cases, optical film 120 includes a binder, a fumed metal oxidesuch as a fumed silica or alumina, and a plurality or network ofinterconnected voids. In such the weight ratio of the fumed metal oxideto the binder is in a range from about 2:1 to about 6:1, or in a rangefrom about 2:1 to about 4:1. In some cases, the weight ratio of thefumed metal oxide to the binder is not less than about 2:1, or not lessthan about 3:1. In some cases, the weight ratio of the fumed metal oxideto the binder is not greater than about 8:1, or not greater than about7:1, or not greater than about 6:1.

Optical film 120 can be any optical film that includes a plurality ofvoids. For example, optical film 120 can be an optical film described inU.S. Provisional Application No. 61/169,466, titled “OPTICAL FILM”,Attorney Docket Number 65062US002, the disclosure of which isincorporated in its entirety herein by reference.

In some cases, optical film 120 can be or include a porous polypropyleneand/or polyethylene film such as a CELGARD film available from CelaneseSeparation Products of Charlotte, N.C.). For example, optical film 120can be or include a CELGARD 2500 film having a thickness of about 25microns and 55% porosity. As another example, optical film 120 can be orinclude a CELGARD M824 film having a thickness of about 12 microns and38% porosity. FIG. 6 is an exemplary optical image of a CELGARD film.

In some cases, optical film 120 can be or include a porous film that ismade by thermally induced phase separation (TIPS), such as those madeaccording to the teachings of U.S. Pat. Nos. 4,539,256 and 5,120,594.TIPS films can have a broad range of microscopic pore sizes. FIG. 7 isan exemplary optical image of a TIPS film.

In some cases, optical film 120 can be or include a porous film that ismade by solvent induced phase separation (SIPS), an exemplary opticalmicrograph of which is shown in FIG. 8. In some cases, optical film 120can be or include a polyvinylidene fluoride (PVDF) porous film.

Optical film 120 can be made using any fabrication method that may bedesirable in an application, such as those described in U.S. Pat. No.8,808,811, and U.S. Publication No. 2012/0021134, the disclosures ofwhich are incorporated in their entirety herein by reference.

Reflective polarizer layer 110 substantially reflects light that has afirst polarization state and substantially transmits light that has asecond polarization state, where the two polarization states aremutually orthogonal. For example, the average reflectance of reflectivepolarizer 110 in the visible for the polarization state that issubstantially reflected by the reflective polarizer is at least about50%, or at least about 60%, or at least about 70%, or at least about80%, or at least about 90%, or at least about 95%. As another example,the average transmittance of reflective polarizer 110 in the visible forthe polarization state that is substantially transmitted by thereflective polarizer is at least about 50%, or at least about 60%, or atleast about 70%, or at least about 80%, or at least about 90%, or atleast about 95%, or at least about 97%, or at least about 98%, or atleast about 99%. In some cases, reflective polarizer 110 substantiallyreflects light having a first linear polarization state (for example,along the x-direction) and substantially transmits light having a secondlinear polarization state (for example, along the z-direction).

Any suitable type of reflective polarizer may be used for reflectivepolarizer layer 110 such as, for example, a multilayer optical film(MOF) reflective polarizer, a diffusely reflective polarizing film(DRPF) having a continuous phase and a disperse phase, such as aVikuiti™ Diffuse Reflective Polarizer Film (“DRPF”) available from 3MCompany, St. Paul, Minn., a wire grid reflective polarizer described in,for example, U.S. Pat. No. 6,719,426, or a cholesteric reflectivepolarizer.

For example, in some cases, reflective polarizer layer 110 can be orinclude an MOF reflective polarizer, formed of alternating layers ofdifferent polymer materials, where one of the sets of alternating layersis formed of a birefringent material, where the refractive indices ofthe different materials are matched for light polarized in one linearpolarization state and unmatched for light in the orthogonal linearpolarization state. In such cases, an incident light in the matchedpolarization state is substantially transmitted through reflectivepolarizer layer 110 and an incident light in the unmatched polarizationstate is substantially reflected by reflective polarizer layer 110. Insome cases, an MOF reflective polarizer layer 110 can include a stack ofinorganic dielectric layers.

As another example, reflective polarizer layer 110 can be or include apartially reflecting layer that has an intermediate on-axis averagereflectance in the pass state. For example, the partially reflectinglayer can have an on-axis average reflectance of at least about 90% forvisible light polarized in a first plane, such as the xy-plane, and anon-axis average reflectance in a range from about 25% to about 90% forvisible light polarized in a second plane, such as the xz-plane,perpendicular to the first plane. Such partially reflecting layers aredescribed in, for example, U.S. Patent Publication No. 2008/064133, thedisclosure of which is incorporated herein in its entirety by reference.

In some cases, reflective polarizer layer 110 can be or include acircular reflective polarizer, where light circularly polarized in onesense, which may be the clockwise or counterclockwise sense (alsoreferred to as right or left circular polarization), is preferentiallytransmitted and light polarized in the opposite sense is preferentiallyreflected. One type of circular polarizer includes a cholesteric liquidcrystal polarizer.

In some cases, reflective polarizer layer 110 can be a multilayeroptical film that reflects or transmits light by optical interference,such as those described in U.S. Publication No. 2011/0222263; U.S. Pat.No. 8,998,776; U.S. Pat. No. 8,917,448; U.S. Pat. No. 8,662,687; and WO2008/144136; all incorporated herein by reference in their entirety.

Substantial portions of each two neighboring major surfaces in opticalconstruction 100 are in physical contact with each other. For example,substantial portions of neighboring major surfaces 122 and 114 ofrespective neighboring layers 120 and 110 in optical construction 100are in physical contact with each other. For example, at least 50%, orat least 60%, or at least 70%, or at least 80%, or at least 90%, or atleast 95% of the two neighboring major surfaces are in physical contactwith each other. For example, in some cases, optical film 120 is coateddirectly on reflective polarizer layer 110.

In general, substantial portions of neighboring major surfaces (majorsurfaces that face each other or are adjacent to each other) of each twoneighboring layers in optical construction 100 are in physical contactwith each other. For example, in some cases, there may be one or moreadditional layers disposed in between reflective polarizer layer 110 andoptical film 120 as shown schematically in, for example, FIGS. 2 and 3.In such cases, substantial portions of neighboring major surfaces ofeach two neighboring layers in optical construction 100 are in physicalcontact with each other. In such cases, at least 50%, or at least 60%,or at least 70%, or at least 80%, or at least 90%, or at least 95% ofthe neighboring major surfaces of each two neighboring layers in theoptical construction are in physical contact with each other.

In the exemplary optical construction 100, optical film 120 physicallycontacts reflective polarizer layer 110. For example, optical film 120can be coated directly on bottom surface 144 of reflective polarizerlayer 11. In some cases, one or more layers can be disposed between thetwo layers. For example, FIG. 2 is a schematic side-view of an opticalconstruction 200 that include an optical adhesive layer 140 disposedbetween optical film 120 and reflective polarizer layer 110 for bondingthe optical film to the polarizer layer.

In some cases, optical adhesive layer 140 has a high specular opticaltransmittance. For example, in such cases, the specular opticaltransmittance of the adhesive layer is not less than about 60%, or notless than about 70%, or not less than about 80%, or not less than about90%.

In some cases, optical adhesive layer 140 is substantially opticallydiffusive and can have a white appearance. For example, in such cases,the optical haze of an optically diffusive adhesive layer 140 is notless than about 30%, or not less than about 30%, or not less than about50%, or not less than about 60%, or not less than about 70%, or not lessthan about 80%, or not less than about 90%, or not less than about 95%.In some case, the diffuse reflectance of the diffusive adhesive layer isnot less than about 20%, or not less than about 30%, or not less thanabout 40%, or not less than about 50%, or not less than about 60%. Insuch cases, the adhesive layer can be optically diffusive by including aplurality of particles dispersed in an optical adhesive where theparticles and the optical adhesive have different indices of refraction.The mismatch between the two indices of refraction can result in lightscattering.

Optical adhesive layer 140 can include any optical adhesive that may bedesirable and/or available in an application. Exemplary opticaladhesives include pressure sensitive adhesives (PSAs), heat-sensitiveadhesives, solvent-volatile adhesives, and UV-curable adhesives such asUV-curable optical adhesives available from Norland Products, Inc.Exemplary PSAs include those based on natural rubbers, syntheticrubbers, styrene block copolymers, (meth)acrylic block copolymers,polyvinyl ethers, polyolefins, and poly(meth)acrylates. As used herein,(meth)acrylic (or acrylate) refers to both acrylic and methacrylicspecies. Other exemplary PSAs include (meth)acrylates, rubbers,thermoplastic elastomers, silicones, urethanes, and combinationsthereof. In some cases, the PSA is based on a (meth)acrylic PSA or atleast one poly(meth)acrylate. Exemplary silicone PSAs include a polymeror gum and an optional tackifying resin. Other exemplary silicone PSAsinclude a polydiorganosiloxane polyoxamide and an optional tackifier.

FIG. 3 is a schematic side-view of an optical construction 300 thatincludes a substrate 160 disposed between optical adhesive layer 140 andoptical film 120. For example, in some cases, optical film 120 is coatedon substrate 160 and optical adhesive layer 140 adheres the coatedsubstrate to reflective polarizer layer 110. As another example, in somecases, optical adhesive layer 140 and optical film 120 are coated onopposite major surfaces of the substrate and the adhesive laminates thetwo-sides coated substrate to the reflective polarizer layer.

Substrate 160 can be or include any material that may be suitable in anapplication, such as a dielectric, a semiconductor, or a metal. Forexample, substrate 160 can include or be made of glass and polymers suchas polyethylene teraphthalate (PET), polycarbonates, and acrylics.Substrate 160 can be rigid or flexible.

Each of optical constructions 100-300 is capable of having a smalloverall thickness while providing high optical gain. As used herein,“gain” or “optical gain” of an optical construction is defined as theratio of the axial output luminance of an optical or display system withthe optical construction to the axial output luminance of the sameoptical or display system without the optical construction. Theinclusion of any of optical constructions 100-300 in a display systemallows for a reduction in the overall size of display system with no orvery little loss in the optical gain of the display system. In somecases, optical constructions 100-300 have optical gains that are notless than about 1.1, or not less than about 1.2, or not less than about1.2, or not less than about 1.25, or not less than about 1.3, or notless than about 1.35, or not less than about 1.4, or not less than about1.45, or not less than about 1.5.

FIG. 9 is a schematic side-view of an optical system 900 centered on anoptical axis 990 for measuring light scattering of an opticallydiffusive film. Optical system 900 includes a half-sphere 910 thatincludes a spherical surface 905, a flat bottom surface 915, and anindex of refraction n_(h), an optically diffusive film 930 laminated tobottom surface 915 via an optical adhesive layer 920, a light source 940emitting light 945, and an optical detector 950 for detecting light thatis scattered by test sample 930.

Light 945 emitted by light source 940 propagates along optical axis 990and is scattered by optically diffusive film 930 inside half-sphere 910which is a high-index medium having the refractive index n_(h).Accordingly, in the presence of the half-sphere, optical system 900measures the scattering of an optically diffusive film in a high-indexmedium. On the other hand, with the half-sphere removed, detector 950detects and measures the light scattering of optically diffusive film950 in a low-index medium (air).

The scattering properties of various porous and non-porous opticallydiffusive films were measured in low-index (air) and high-index (n_(h))media using an Imaging Sphere (available from Radiant Imaging Inc.,Duvall, Wash.). The Imaging Sphere was similar to optical system 900. Ahalf-sphere of solid acrylic with a diameter of 63 mm was placed insidethe Imaging Sphere with the flat bottom surface against the sample portwhere film samples could be adhered to the center of the half-sphere.The index of refraction of the hemisphere is about 1.49. Incident light945 was white light with a beam diameter of about 4 mm. For eachoptically diffusive film, first, the scattering of the film was measuredin air. Next, the film was laminated to bottom surface 915 ofhalf-sphere 910 via optical adhesive layer 920 (optically clear adhesiveOCA 8171 available from 3M Company, St. Paul Minn.) and the scatteringwas measured in the acrylic medium.

FIG. 10 shows the scattering distribution measured for a porousoptically diffusive film and a non-porous optically diffusive film inair. The horizontal axis in FIG. 10 is the scattering angle θ measuredfrom optical axis 990 and the vertical axis is the intensity ofscattered light. Curve 1010 is the measured scattering distributionmeasured for the non-porous optically diffusive film OF7 described inExample 13, and Curve 1020 is the measured scattering distribution forthe porous optical film OF3 also described in Example 13. Both filmshave the same scattering width W₁.

FIG. 11 shows the scattering distribution measured for the two films inthe high-index medium. Curve 1110 is the measured scatteringdistribution measured for the non-porous optically diffusive film andCurve 1120 is the measured scattering distribution for the porousoptically diffusive film. The non-porous diffusive film had a scatteringdistribution width W₂ that substantially greater than the scatteringdistribution width W3 of the porous diffusive film. Hence, althoughporous and non-porous optically diffusive films with similartransmittance and reflectance properties have similar scatteringdistribution properties in air, the porous optically diffusive filmshave substantially narrower scattering widths in high-index media thannon-porous optically diffusive films.

FIG. 4A is a schematic side-view of a display system 400 that includes aliquid crystal panel 410 that is laminated to an optical construction405 via an optical adhesive layer 420, and a light source 480 that emitslight 462 towards optical construction 405.

Optical construction 405 includes an optical diffuser layer 450, anoptical film 440 disposed on the optical diffuser layer, and areflective polarizer layer 430 disposed on the optical film. Lightsource 480 includes a plurality of lamps 460 that face opticalconstruction 405 and a light reflecting cavity 470 that includes a backreflector 474 and side reflectors 472 and 476. At least one of the lamps460 is at least partially housed within reflective optical cavity 470.Light reflecting cavity 470 collects light that is emitted by lamps 460in directions other than along the optical construction (positivey-direction), such as light that is emitted along the x- or negativey-direction and redirects such light toward optical construction 405along the positive y-axis. Display systems such as display system 400where lamps 460 face the major surfaces of the various layers in thesystem, are generally referred to as direct-lit display systems.

Optical film 440 has an index of refraction in the visible range of theelectromagnetic spectrum that is less than about 1.4, or less than about1.35, or less than about 1.30, or less than about 1.2, or less thanabout 1.15, or less than about 1.1. Optical film 440 has a small opticalhaze. For example, the optical haze of optical film 440 is not greaterthan about 10%, or not greater than about 8%, or not greater than about6%, or not greater than about 5%, or not greater than about 4%, or notgreater than about 3%, or not greater than about 2%, or not greater thanabout 1%, or not greater than about 0.5%. Optical film 440 has a highaverage specular optical transmittance in the visible. For example, theaverage specular optical transmittance of the optical film is greaterthan about 70%, or greater than about 75%, or greater than about 80%, orgreater than about 85%, or greater than about 90%, or greater than about95%.

Optical film 440 can be any optical film that includes a plurality ofvoids and has low haze and refractive index. For example, optical film440 can be or include any optical film or any combination of opticalfilms disclosed herein. For example, optical film 440 can be similar tooptical film 120.

Optical film 440 promotes total internal reflection at a major surface432 of reflective polarizer layer 430. For example, in some cases, theoptical film promotes the total internal reflection of an incident lightray 434 having an incident angle θ as reflected light ray 436, where inthe absence of the optical film, at least a significant portion ofincident light ray 434 would leak through, or be transmitted by,reflective polarizer layer 430 as leaked light ray 435.

Optical diffuser 450 has the primary functions of hiding or maskinglamps 460 and homogenizing light 462 that is emitted by light source480. Optical diffuser layer 450 has a high optical haze and/or a highdiffuse optical reflectance. For example, in some cases, the opticalhaze of the optical diffuser is not less than about 40%, or not lessthan about 50%, or not less than about 60%, or not less than about 70%,or not less than about 80%, or not less than about 85%, or not less thanabout 90%, or not less than about 95%. As another example, the diffuseoptical reflectance of the optical diffuser is not less than about 30%,or not less than about 40%, or not less than about 50%, or not less thanabout 60%.

Optical diffuser 450 can be or include any optical diffuser that may bedesirable and/or available in an application. For example, opticaldiffuser 450 can be or include a surface diffuser, a volume diffuser, ora combination thereof. For example, optical diffuser 450 can include aplurality of particles having a first index of refraction n₁ dispersedin a binder or host medium having a different index of refraction n₂,where the difference between the two indices of refraction is at leastabout 0.01, or at least about 0.02, or at least about 0.03, or at leastabout 0.04, or at least about 0.05.

Reflective polarizer layer 430 substantially reflects light that has afirst polarization state and substantially transmits light that has asecond polarization state, where the two polarization states aremutually orthogonal. Any suitable type of reflective polarizer may beused for reflective polarizer layer 430. For example, reflectivepolarizer layer 430 can be similar to reflective polarizer layer 110.

Substantial portions of each two neighboring major surfaces in opticalconstruction 405 are in physical contact with each other. For example,at least 50%, or at least 60%, or at least 70%, or at least 80%, or atleast 90%, or at least 95% of each two neighboring major surfaces in theoptical construction are in physical contact with each other. Forexample, in some cases, a layer in optical construction 405 is eitherlaminated to or coated on a neighboring layer.

In general, substantial portions of neighboring major surfaces (majorsurfaces that face each other or are adjacent to each other) of each twoneighboring layers in optical construction 405 are in physical contactwith each other. For example, in some cases, there may be one or moreadditional layers disposed in between reflective polarizer layer 430 andoptical film 440, but, in such cases, substantial portions ofneighboring major surfaces of each two neighboring layers in opticalconstruction 405 are in physical contact with each other. In such cases,at least 50%, or at least 60%, or at least 70%, or at least 80%, or atleast 90%, or at least 95% of the neighboring major surfaces of each twoneighboring layers in the optical construction are in physical contactwith each other.

Liquid crystal panel 410 includes, not expressly shown in FIG. 4A, alayer of liquid crystal disposed between two panel plates, an upperlight absorbing polarizer layer disposed above the liquid crystal layer,and a lower absorbing polarizer disposed below the liquid crystal layer.The upper and lower light absorbing polarizers and the liquid crystallayer, in combination, control the transmission of light from reflectivepolarizer layer 430 through liquid crystal panel 410 to a viewer 490.

Display system 400 is capable of having a small overall thickness whileproviding high optical gain. The inclusion of optical film 440 allowsfor a reduction in the overall size of display system 400 with no orvery little loss in the optical gain of the display system. In somecases, display system 400 has an optical gain of at least about 1.1, orat least about 1.2, or at least about 1.2, or at least about 1.25, or atleast about 1.3, or at least about 1.35, or at least about 1.4, or atleast about 1.45, or at least about 1.5.

FIG. 4B is a schematic side-view of a display system 401 that is similarto display system 400 except that optical construction 405 is replacedwith an optical construction 406 that includes reflective polarizerlayer 430 disposed on an optical film 445. Reflective polarizer layer430 includes a first major surface 441 and optical film 445 includes asecond major surface 442. Substantial portions of neighboring majorsurfaces 441 and 442 of respective neighboring layers 430 and 445 inoptical construction 406 are in physical contact with each other. Forexample, at least 50%, or at least 60%, or at least 70%, or at least80%, or at least 90%, or at least 95% of the two neighboring majorsurfaces are in physical contact with each other.

In general, substantial portions of neighboring major surfaces (majorsurfaces that face each other or are adjacent to each other) of each twoneighboring layers in optical construction 406 are in physical contactwith each other. For example, in some cases, there may be one or moreadditional layers, such as an adhesive layer and/or a substrate layernot expressly shown in FIG. 4B, disposed in between reflective polarizer430 and optical film 445. In such cases, substantial portions ofneighboring major surfaces of each two neighboring layers in opticalconstruction 406 are in physical contact with each other. In such cases,at least 50%, or at least 60%, or at least 70%, or at least 80%, or atleast 90%, or at least 95% of the neighboring major surfaces of each twoneighboring layers in the optical construction are in physical contactwith each other.

Optical film 445 includes a plurality of voids, and has high opticalhaze and a narrow scattering distribution width in high-index media. Forexample, optical film 445 has an optical haze that is not less thanabout 20%, or not less than about 30%, or not less than about 40%, ornot less than about 50%, or not less than about 60%, or not less thanabout 70%, or not less than about 80%, or not less than about 90%, ornot less than about 95%. Optical film 445 can be any optical filmdisclosed herein. For example, optical film 445 can be similar tooptical film 120.

Optical film 445 advantageously allows for reduction of the overallthickness and manufacturing cost of display system 401. At the sametime, the optical film 445 has high optical haze and reflectance.Furthermore, the optical film provides for large optical gain by virtueof having a narrow scattering distribution width in high-index media.For example, the optical gain of optical construction 406 is at leastabout 1.1, or at least about 1.15, or at least about 1.2, or at leastabout 1.25, or at least about 1.3, or at least about 1.35, or at leastabout 1.4, or at least about 1.45, or at least about 1.5.

FIG. 5A is a schematic side-view of a display system 500 that includes aliquid crystal panel 517 and an optical construction 505 that islaminated to a light source or backlight 580 via an optical adhesivelayer 520.

Optical construction 505 includes an optical diffuser layer 550 similarto optical diffuser layer 450, an optical film 540 similar to opticalfilm 440 and disposed on the optical diffuser layer, and a reflectivepolarizer layer 530 similar to reflective polarizer layer 530 anddisposed on the optical film. Light source 580 includes a lightguide510, a lamp 560 that is placed along an edge 514 of the light guide andhoused inside a side reflector 572, and a back reflector 570. Ingeneral, backlight 580 can include one or more lamps placed along one ormore edges of lightguide 510.

Light 562 emitted from lamp 560 enters lightguide 510 through edge 514of the lightguide. The entered light propagates in lightguide 510 in thegeneral x-direction by reflection, such as by total internal reflection,at major surfaces 516 and 518. Major surface 518 includes a plurality oflight extractors 512 that are capable of extracting light thatpropagates in the lightguide. In general, the spacing betweenneighboring light extractors can be different at different locations onmajor surface 518. Furthermore, the shape, respective heights, and/orsize of the light extractors can be different for different lightextractors. Such a variation can be useful in controlling the amount oflight extracted at different locations on major surface 518.

Back reflector 570 receives light that is emitted by the light guideaway from optical construction 505 along the negative y-direction andreflects the received light towards the optical construction. Displaysystems such as display system 500 where lamps 560 are placed along theedges of a lightguide, are generally referred to as edge-lit or backlitdisplays or optical systems.

Optical film 540 includes a plurality of voids and has an effectiveindex of refraction that is less than about 1.4, or less than about1.35, or less than about 1.30, or less than about 1.2, or less thanabout 1.15, or less than about 1.1. Optical film 540 has a small opticalhaze. For example, the optical haze of optical film 540 is not greaterthan about 20%, or not greater than about 15%, or not greater than about10%, or not greater than about 8%, or not greater than about 6%, or notgreater than about 5%, or not greater than about 4%, or not greater thanabout 3%, or not greater than about 2%. Optical film 540 has a highaverage specular transmittance in the visible. For example, the averagespecular transmittance of the optical film is at least greater thanabout 70%, or at least greater than about 75%, or at least greater thanabout 80%, or at least greater than about 85%, or at least greater thanabout 90%, or at least greater than about 95%.

Optical film 540 can be or include any optical film or optical filmsdisclosed herein. For example, optical film 540 can be similar tooptical film 120. Optical film 540 promotes total internal reflection ata major surface 532 of reflective polarizer layer 530. For example, insome cases, the optical film promotes the total internal reflection ofan incident light ray 534 having a large incident angle θ₁ as reflectedlight ray 536, where in the absence of the optical film, at least asignificant portion of incident light ray 534 would leak through, or betransmitted by, reflective polarizer layer 530 as leaked light ray 535.

Optical diffuser 550 has the primary functions of effectively hidinglamp 560 and extractors 512, and homogenizing light that exitslightguide 510. Optical diffuser layer 550 has a high optical hazeand/or a high diffuse optical transmittance. For example, in some cases,the optical haze of the optical diffuser is not less than about 40%, ornot less than about 50%, or not less than about 60%, or not less thanabout 70%, or not less than about 80%, or not less than about 85%, ornot less than about 90%, or not less than about 95%.

Optical diffuser 550 can be or include any optical diffuser that may bedesirable and/or available in an application. For example, opticaldiffuser 450 can be similar to optical diffuser 450.

Display system 500 is capable of having a small overall thickness whileproviding high optical gain. The inclusion of optical film 540 allowsfor a reduction in the overall size of display system 500 with no orvery little loss in the optical gain of the display system. In somecases, display system 500 has an optical gain of at least about 1.1, orat least about 1.2, or at least about 1.2, or at least about 1.25, or atleast about 1.3, or at least about 1.35, or at least about 1.4, or atleast about 1.45, or at least about 1.5.

FIG. 5B is a schematic side-view of a display system 501 that includesan optical construction 506 that includes lightguide 510, an opticalfilm 555 disposed on the lightguide, and reflective polarizer 430disposed on the optical film. Reflective polarizer layer 530 includes afirst major surface 531 that faces optical film 555, optical film 555includes a first major surface 557 facing the lightguide and a secondmajor surface 556 facing the reflective polarizer layer, and lightguide510 includes an exit surface 511 facing the optical film. Substantialportions of neighboring major surfaces 531 and 556 of the two respectiveneighboring layers 530 and 555 in optical construction 506 are inphysical contact with each other. For example, at least 50%, or at least60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%of the two neighboring major surfaces are in physical contact with eachother.

Substantial portions of neighboring major surfaces 557 and 511 of thetwo respective neighboring layers 555 and 510 in optical construction506 are in physical contact with each other. For example, at least 50%,or at least 60%, or at least 70%, or at least 80%, or at least 90%, orat least 95% of the two neighboring major surfaces are in physicalcontact with each other.

In general, substantial portions of neighboring major surfaces (majorsurfaces that face each other or are adjacent to each other) of each twoneighboring layers in optical construction 506 are in physical contactwith each other. For example, in some cases, there may be one or moreadditional layers, such as an adhesive layer and/or a substrate layernot expressly shown in FIG. 5B, disposed in between reflective polarizer530 and optical film 555. In such cases, substantial portions ofneighboring major surfaces of each two neighboring layers in opticalconstruction 506 are in physical contact with each other. In such cases,at least 50%, or at least 60%, or at least 70%, or at least 80%, or atleast 90%, or at least 95% of the neighboring major surfaces of each twoneighboring layers in the optical construction are in physical contactwith each other.

Optical film 555 can be any optical film disclosed herein. For example,optical film 555 can be similar to optical film 445. Optical film hashigh optical haze and is capable of preserving or maintaining theoptical gain of display system 501 by virtue of having a narrowscattering distribution in high-index media. For example, the opticalgain of the optical construction 506 is at least about 1.1, or at leastabout 1.2, or at least about 1.2, or at least about 1.25, or at leastabout 1.3, or at least about 1.35, or at least about 1.4, or at leastabout 1.45, or at least about 1.5.

Optical film 555 manifests some low-refractive-index-like properties.For example, optical diffuser 555 can support TIR or enhance internalreflection. For example, a light ray 512 that is incident on theinterface between the optical diffuser layer and the reflectivepolarizer layer with an incident angle θ₁, under goes TIR or enhancedreflection. As another example, a light ray 511 that is incident on theinterface between the optical film and the lightguide with an incidentangle θ₂, under goes TIR or enhanced reflection.

FIG. 17 is a schematic side-view of a display system 1700 that includesback reflector 570, lightguide 510 separated from the back reflector byan air gap 1710, a turning film disposed on the lightguide and separatedfrom the light by an air gap 1720, an optical adhesive layer 1740disposed on the turning film, an optical film 1750 disposed on theoptical adhesive layer, a reflective polarizer layer 1760 disposed onthe optical film, an optical adhesive layer 1770 disposed on reflectivepolarizer layer and liquid crystal panel 517 disposed on the opticaladhesive layer.

Turning film 1730 redirects light that it receives from lightguide 510.In some cases, such as when display system 1700 includes an obliquelyilluminated backlight, turning film 1730 has the optical effect ofredirecting the bright off-axis lobes of the display system towards theviewing axis of the display. Turning film 1730 includes a plurality ofstructures 1732 facing lightguide 1732 and disposed on a substrate 1734.In some cases, structures 1732 can be prismatic. For example, in somecases, turning film 1730 can be an inverted prismatic brightnessenhancement film.

Optical film 1750 can be any optical film disclosed herein. For example,optical film 1750 can be similar to optical film 555 or 540. In general,optical film 1750 can have any optical haze that may be desirable in anapplication. For example, in some cases, optical film 1750 can have anoptical haze that is in a range from about 5% to about 70%, or fromabout 10% to about 60%, or from about 10% to about 50%, or from about10% to about 40%, or from about 15% to about 35%, or from about 20% toabout 30%. In some cases, the haze of the optical film is not greaterthan about 20%. In some cases, the haze of the optical film is not lessthan about 20%.

In general, lightguide 510 can be made of any material and can have anyshape that may be desirable in an application. For example, lightguide510 can be made of polycarbonate or acrylic, and may be rectangular andwedge shaped in cross-section. Lightguide 510 can includes extractionfeatures not expressly shown in FIG. 17. The extraction features and thelightguide can, in some cases, be molded during an injection moldingprocess.

Optical adhesive layers 1770 and 1740 can be similar to optical adhesivelayer 420. In some cases, optical adhesive layer 1770 and/or 1740 can beoptically diffusive. Reflective polarizer layer can be similar toreflective polarizer layer 430.

FIG. 18 is a schematic side-view of a display system 1800 that includesan optical stack 1810 facing lightguide 510. Optical stack 1810 includesoptical diffuser layer 510, reflective polarizer layer 530, optical film540, and optical adhesive layer 520, and liquid crystal panel 517.

Liquid crystal panel 517 includes, not expressly shown in FIG. 18, alayer of liquid crystal disposed between two panel plates, an upperlight absorbing polarizer layer disposed above the liquid crystal layer,and a lower absorbing polarizer disposed below the liquid crystal layer.The upper and lower light absorbing polarizers and the liquid crystallayer, in combination, control the transmission of light from reflectivepolarizer layer 530 through liquid crystal panel 410 to a viewer facingthe display system.

Optical stack 1810 includes at least one light absorbing polarizer layerthat is part of liquid crystal panel 517 and has a pass-axis that is inthe same direction as the pass-axis of reflective polarizer layer 530.

In general, optical film 540, reflective polarizer layer 530, andoptical diffuser layer 550 can be disposed in any order in optical stack1810 that may be desirable in an application. Furthermore, optical film540 and optical diffuser layer 550 can have any optical haze or diffusereflectance that may be desirable in an application. For example, insome cases, the reflective polarizer layer can be disposed between theliquid crystal panel (or the linear absorbing polarizer) and the opticalfilm. In such cases, the optical film can have a low or high opticalhaze. For example, the optical film can have an optical haze that is notgreater than about 20%, or not greater than about 15%, or not greaterthan about 10%, or not greater than about 5%, or not greater than about4%, or not greater than about 3%, or not greater than about 2%, or notgreater than about 1%. As another example, the optical film can have anoptical haze that is not less than about 20%, or not less than about30%, or not less than about 40%, or not less than about 50%, or not lessthan about 60%, or not less than about 70%, or not less than about 80%,or not less than about 90%, or not less than about 95%.

In some cases, the optical film can be disposed between the absorbingpolarizer (or the liquid crystal panel) liquid crystal panel and thereflective polarizer layer. In such cases, the optical film can have alow or high optical haze. For example, the optical film can have anoptical haze that is not greater than about 20%, or not greater thanabout 15%, or not greater than about 10%, or not greater than about 5%,or not greater than about 4%, or not greater than about 3%, or notgreater than about 2%, or not greater than about 1%. As another example,the optical film can have an optical haze that is not less than about20%, or not less than about 30%, or not less than about 40%, or not lessthan about 50%, or not less than about 60%, or not less than about 70%,or not less than about 80%, or not less than about 90%, or not less thanabout 95%.

In some cases, the optical film can be disposed between the reflectivepolarizer layer and the optical diffuser layer. In some cases, thereflective polarizer layer is disposed between the optical film and theoptical diffuser layer.

Substantial portions of each two neighboring major surfaces in opticalstack 1810 are in physical contact with each other. For example,substantial portions of neighboring major surfaces 1820 and 1815 ofrespective neighboring layers 540 and 530 in optical stack 1810 are inphysical contact with each other. For example, at least 50%, or at least60%, or at least 70%, or at least 80%, or at least 90%, or at least 95%of the two neighboring major surfaces are in physical contact with eachother. For example, in some cases, optical film 540 is coated directlyon reflective polarizer layer 530.

In general, substantial portions of neighboring major surfaces (majorsurfaces that face each other or are adjacent to each other) of each twoneighboring layers in optical stack 1810 are in physical contact witheach other. For example, in some cases, there may be one or moreadditional layers disposed in between reflective polarizer layer 530 andoptical film 540, not shown expressly in FIG. 18. In such cases,substantial portions of neighboring major surfaces of each twoneighboring layers in optical stack 1810 are in physical contact witheach other. In such cases, at least 50%, or at least 60%, or at least70%, or at least 80%, or at least 90%, or at least 95% of theneighboring major surfaces of each two neighboring layers in the opticalconstruction are in physical contact with each other.

Some of the advantages of the disclosed films, layers, constructions,and systems are further illustrated by the following examples. Theparticular materials, amounts and dimensions recited in this example, aswell as other conditions and details, should not be construed to undulylimit the present invention.

In the examples, the index of refraction was measured using a MetriconModel 2010 Prism Coupler (available from Metricon Corp., Pennington,N.J.). Optical transmittance and haze were measured using a Haze-guardPlus haze meter (available from BYK-Gardiner, Silver Springs, Md.).

Example A

A coating solution “A” was made. First, a “906” composition (availablefrom 3M Company, St. Paul, Minn.) was obtained. The 906 compositionincluded: 18.4 wt % 20 nm silica particles (Nalco 2327) surface modifiedwith methacryloyloxypropyltrimethoxysilane (acrylate silane), 25.5 wt %Pentaerthritol tri/tetra acrylate (PETA), 4.0 wt %N,N-dimethylacrylamide (DMA), 1.2 wt % Irgacure 184, 1.0 wt % Tinuvin292, 46.9 wt % solvent isopropanol, and 3.0 wt % water. The 906composition was approximately 50% solid by weight. Next, the 906composition was diluted to 35 wt % solid with solvent 1-methoxy2-propanol resulting in coating solution A.

Example B

A coating solution “B” was made. First, 360 g of Nalco 2327 colloidalsilica particles (40% wt solid and an average particle diameter of about20 nanometers) (available from Nalco Chemical Company, Naperville Ill.)and 300 g of solvent 1-methoxy-2-propanol were mixed together underrapid stirring in a 2-liter three-neck flask that was equipped with acondenser and a thermometer. Next, 22.15 g of Silquest A-174 silane(available from GE Advanced Materials, Wilton Conn.) was added. Themixture was stirred for 10 min. Next, an additional 400 g of1-methoxy-2-propanol was added. The mixture was heated at 85° C. for 6hours using a heating mantle. The resulting solution was allowed to cooldown to room temperature. Next, most of water and 1-methoxy-2-propanolsolvents (about 700 g) were removed using a rotary evaporator under a60° C. water-bath. The resulting solution was 44% wt A-174 modified 20nm silica clear dispersed in 1-methoxy-2-propanol. Next, 70.1 g of thissolution, 20.5 g of SR 444 (available from Sartomer Company, Exton Pa.),1.375 g of photoinitiator Irgacure 184 (available from Ciba SpecialtyChemicals Company, High Point N.C.), and 80.4 g of isopropyl alcoholwere mixed together by stirring to form a homogenous coating solution B.

Example C

A coating solution “C” was made. First, 100 g of Cabot PG002 fumedsilica (available from Cabot Corporation, Billerica Mass.) was added toa 500 ml 3-neck flask that was equipped with a condenser, a stir bar andstir plate, a temperature controller and a heating mantle. Next, apremix of 3.08 g Silquest A174 and 100 g of 1-methoxy-2-propanol wasadded to the flask. The mixture was stirred at 80° C. for about 16hours. The resulting mixture had low viscosity and had a hazytranslucent appearance. The mixture was then cooled to room temperature.

Next, the mixture was transferred to a 500 ml one-neck distillationflask. The water was removed from the mixture by alternate vacuumdistillation and using a rotary evaporator (Rotavapor available fromBUCHI Corporation, New Castle, Del.) and addition of 160 g of1-methoxy-2-propanol. The mixture was further concentrated by vacuumdistillation resulting in 78.4 g of a low viscosity, hazy, translucentdispersion with 25.6 wt % solids.

Next, 78.4 g of A-174 modified fumed Silica, 13.38 g of SR444, 0.836 gof photoinitiator Irgcure 184, and 19.7 g of isopropyl alcohol weremixed and stirred resulting in a homogenous coating solution “C”.

Example D

A coating solution “D” was made. First, in a 2 liter three-neck flask,equipped with a condenser and a thermometer, 960 grams of IPA-ST-UPorganosilica elongated particles (available from Nissan Chemical Inc.,Houston, Tex.), 19.2 grams of deionized water, and 350 grams of1-methoxy-2-propanol were mixed under rapid stirring. The elongatedparticles had a diameter in a range from about 9 nm to about 15 nm and alength in a range of about 40 nm to about 100 nm. The particles weredispersed in a 15.2% wt IPA. Next, 22.8 grams of Silquest A-174 silane(available from GE Advanced Materials, Wilton, Conn.) was added to theflask. The resulting mixture was stirred for 30 minutes.

The mixture was then kept at 81° C. for 16 hours. Next, the solution wasallowed to cool down to room temperature. Next, about 950 grams of thesolvent in the solution were removed using a rotary evaporator under a40° C. water-bath, resulting in a 41.7% wt A-174-modified elongatedsilica clear dispersion in 1-methoxy-2-propanol.

Next, 407 grams of this clear dispersion, 165.7 grams of SR 444(available from Sartomer Company, Exton, Pa.), 8.28 grams ofphotoinitiator Irgacure 184 and 0.828 grams of photoinitiator Irgacure819 (both available from Ciba Specialty Chemicals Company, High PointN.C.), and 258.6 grams of isopropyl alcohol were mixed together andstirred resulting in a homogenous coating solution of 40% solids. Next,300 grams of this solution was mixed with 100 grams of isopropyl alcoholresulting in a coating solution of 30% solids.

Example E

A coating procedure “E” was developed. First, a coating solution wassyringe-pumped at a rate of 3 cc/min into a 10.2 cm (4-inch) wideslot-type coating die. The slot coating die uniformly distributed a 10.2cm wide coating onto a substrate moving at 152 cm/min (5 ft/min).

Next, the coating was polymerized by passing the coated substratethrough a UV-LED cure chamber that included a quartz window to allowpassage of UV radiation. The UV-LED bank included a rectangular array of160 UV-LEDs, 8 down-web by 20 cross-web (approximately covering a 10.2cm×20.4 cm area). The LEDs (available from Cree, Inc., Durham N.C.)operated at a nominal wavelength of 385 nm, and were run at 45 Volts at8 Amps, resulting in a UV-A dose of 0.212 joules per square cm. TheUV-LED array was powered and fan-cooled by a TENMA 72-6910 (42V/10 A)power supply (available from Tenma, Springboro Ohio). The UV-LEDs werepositioned above the quartz window of the cure chamber at a distance ofapproximately 2.5 cm from the substrate. The UV-LED cure chamber wassupplied with a flow of nitrogen at a flow rate of 46.7 liters/min (100cubic feet per hour) resulting in an oxygen concentration ofapproximately 150 ppm in the cure chamber.

After being polymerized by the UV-LEDs, the solvent in the cured coatingwas removed by transporting the coated substrate to a drying oven at150° F. for 2 minutes at a web speed of 5 ft/min. Next, the driedcoating was post-cured using a Fusion System Model I300P configured withan H-bulb (available from Fusion UV Systems, Gaithersburg Md.). The UVFusion chamber was supplied with a flow of nitrogen that resulted in anoxygen concentration of approximately 50 ppm in the chamber.

Example F

A coating procedure “F” was developed. First, a coating solution wassyringe-pumped at a rate of 5.4 cc/min into a 20.3 cm (8-inch) wideslot-type coating die. The slot coating die uniformly distributed a 20.3cm wide coating onto a substrate moving at 5 ft/min (152 cm/min).

Next, the coating was polymerized by passing the coated substratethrough a UV-LED cure chamber that included a quartz window to allowpassage of UV radiation. The UV-LED bank included a rectangular array of352 UV-LEDs, 16 down-web by 22 cross-web (approximately covering a 20.3cm×20.3 cm area). The UV-LEDs were placed on two water-cooled heatsinks. The LEDs (available from Cree, Inc., Durham N.C.) operated at anominal wavelength of 395 nm, and were run at 45 Volts at 10 Amps,resulting in a UV-A dose of 0.108 joules per square cm. The UV-LED arraywas powered and fan-cooled by a TENMA 72-6910 (42V/10 A) power supply(available from Tenma, Springboro Ohio). The UV-LEDs were positionedabove the cure chamber quartz window at a distance of approximately 2.54cm from the substrate. The UV-LED cure chamber was supplied with a flowof nitrogen at a flow rate of 46.7 liters/min (100 cubic feet per hour)resulting in an oxygen concentration of approximately 150 ppm in thecure chamber.

After being polymerized by the UV-LEDs, the solvent in the cured coatingwas removed by transporting the coating to a drying oven operating at150° F. for 2 minutes at a web speed of 5 ft/min. Next, the driedcoating was post-cured using a Fusion System Model I300P configured withan H-bulb (available from Fusion UV Systems, Gaithersburg Md.). The UVFusion chamber was supplied with a flow of nitrogen that resulted in anoxygen concentration of approximately 50 ppm in the chamber.

Example G

Coating solutions 1-9 were made using hydrophobic resins listed in TableI. For each coating solution, the resin and the fumed silica (availableas TS-530 from Cabot Corporation, Billerica Mass.) at the weight ratiospecified in Table I were mixed with the corresponding solvent alsospecified in Table I. The resin had a wt-part of 1. For example, forcoating solution 1, the weight ratio of resin FC2145 to fumed silica was1:5.

The resin used in coating solutions 1, 2, and 9 was DyneonFluoroelastomer Copolymer FC2145 (available from Dyneon LLC, OakdaleMinn.). The resin used in coating solutions 3 and 4 was SPU-5k which wasa silicone polyurea formed from the reaction between an α ω aminoproplypolydiemthyl siloxane and m-tetramethyl xylene diisocyante as generallydescribed in U.S. Pat. No. 6,355,759, Example #23. The resin used incoating solutions 5 and 6 was SR-351, a UV-polymerizable monomer(available from Sartomer Company, Exton Pa.). The resin used in coatingsolutions 7 and 8 was Ebecryl 8807 (EB-8807), a UV-polymerizable monomer(available from Cytec Corporation, West Paterson N.J.). Samples 5-8 wereUV curable and included 1% by weight of Esacure KB-1 photoinitiator inmethylethyl ketone (available from Lamberti USA, Conshohocken Pa.).

For each coating solution, the solvent was either isopropyl alcohol(IPA) or methanol (MeOH). The mixing of the resin, the fumed silica, andthe solvent was done in a 300 mL stainless steel beaker. The fumedsilica was dispersed in the resin using a Ross 100-LC single stage highshear mixer with a single stage slotted head rotor (available fromCharles Ross and Sons, Hauppauge N.Y.) for about 3 minutes at 1200 rpm.Next, the resulting foam was allowed to settle. Next, the solid weightpercentage was adjusted to 12% by adding more of the same solventresulting in coating solutions 1-9.

Next, a coating method was developed for each coating solution. First,the coating solution was coated on a PVC Vinyl organosol substrate(available as Geon 178 from PolyOne, Avon Lake Ohio) using a roundwire-rod (available as a Meyer rod from RD Specialties, Webster N.Y.),where the size of the rod is specified in Table I. The wet coatingthickness was dictated by the wire-rod number. A number 30 wire-rodresulted in a wet coating thickness of approximately 75.2 microns, and anumber 15 wire-rod resulted in a wet coating thickness of approximately38.1 microns.

Coated samples 1-4 and 9 were dried at room temperature for 25 minutes.Coated samples 5-8 were cured with UV radiation using a Fusion SystemsLight Hammer UV system (available from Fusion Systems Inc, Gaithersburg,Md.) that was equipped with a 500 Watt H-bulb. The coatings were curedwith a single exposure at 40 feet per minute (12.3 meters per minute)which corresponded to a UV-B dose of about 49 mille-joules per squarecm.

TABLE I Formulation and coating parameters for Example G Coating Resinf-SiO₂ Coating Photo Solution # (wt-part = 1) (wt-part) Solvent RodInitiator 1 FC2145 5 MeOH 30 — 2 FC2145 5 MeOH 15 — 3 SPU-5k 5 IPA 30 —4 SPU-5k 5 IPA 15 — 5 SR-351 5 IPA 30 1% KB-1 6 SR-351 5 IPA 15 1% KB-17 EB-8807 5 IPA 30 1% KB-1 8 EB-8807 5 IPA 15 1% KB-1 9 FC2145 0 MeOH 30—

Example H

A coating solution was made by mixing hydrophilic polyvinylalcohol(available as Poval PVA-235 from Kuraray America, Houston Tex.) andfumed silica (available as Cabo-O-Sperse PG022 from Cabot Corporation,Billerica Mass.). Next, 14.28 g of PVA-235 (7% wt solid in water) and 20g of PG022 (20% wt in water), 0.25 g of Tergitol Min-Foam XL (availablefrom Dow Chemical Company, Midland Mich.), 7.39 g of water, and 2.9 g ofboric acid (5% wt in water) were mixed together and stirred in a beaker.

Next, the coating solution was applied on a 5 mil thick PET film using anumber-30 wire-wound rod (available from RD Specialties, Webster, N.Y.).Next, the coated film was dried at 100° C. for 1 min.

Example I

First, a coating solution was made. In a 2 liter tree-neck flask,equipped with a condenser and a thermometer, 401.5 grams of Nalco 2327silica particles, 11.9 grams of Trimethoxy (2,4,4 trimethypentyl)silane, 11.77 grams of (Triethoxysilyl) propionitrile, and 300 grams of1-methoxy-2-propanol were mixed together and stirred. The flask wassealed and heated at 80° C. for 16 hours. Next, 100 grams of thissolution and 30 grams of SR444 were added to a 250 milliliterround-bottom flask. The solvents in the solution were removed by rotaryevaporation. Next, 10 grams of isopropanol was added to the flask. Next,20 grams of 1-methoxy-2-propanol, 40 grams of isopropanol, 0.125 gramsof Irgcure 819, and 1.25 grams of Irgcure 184 were added to thesolution, resulting in a 30% by weight coating solution.

Example 1

A reference optical construction 2500, a side-view of which is shownschematically in FIG. 12, was made. First, volume diffuser 450 was made.A mixture was made that included: Polystyrene beads with an averagediameter of about 6 microns (available as SBX-6 from Sekisui PlasticsCo, Osaka, Japan) at 26% by weight, resin PH-6010 (available as Photomer6010 from Cognis North America, Cincinnati Ohio) at 9% by weight, resinsSR9003 at 4.6% by weight and SR833 at 4% by weight (both available fromSartomer Company, Exton Pa.), solvent Dowanol PM (available from DowChemical Company, Midland Mich.) at 60% by weight, and photoinitiatorDarocur 4265 (available from Ciba Specialty Chemicals Company, HighPoint N.C.) at 0.4% by weight. The mixture was stirred in a high shearmixer with the beads added last to the mixture.

Next, 9w162 TiO2 dispersion (available from Penn Color) at 2.6% wt wasadded to the above mixture. The resulting solution was then coated,dried and uv-cured to a dry thickness of about 39 microns on a 0.254 mmthick polyester (PET) film 2510. The resulting volume optical diffuser450 had a total optical transmission of about 50%, an optical haze ofabout 100%, and a clarity of about 3%.

Next, the substrate side of the optical diffuser was laminated to aDBEF-Q reflective polarizer layer 430 (available as Vikuiti DBEF-Q from3M Company, St. Paul, Minn.) via an optically clear adhesive 2520(available as OCA 8171 from 3M Company, St. Paul Minn.). The opticaladhesive has an index of refraction of about 1.48. Next, the other sideof the reflective polarizer layer was laminated to a linear absorbingpolarizer 2540 (available as SR5618 from San Ritz Corporation, TokyoJapan). FIG. 12 shows the configuration of the resulting film stack.

The axial luminance (cd/m²), integrated intensity (lm/m²), and halfbrightness angles (degrees) in the up and down directions of the opticalconstruction were measured using a Schott-Fostec-DCR light source(available from Schott-Fostec LLC, Auburn N.Y.) for illuminating thereference optical construction from the diffuser side, and an AutronicConoscope Conostage 3 (available from Autronic-Melchers GmbH, Karlsruhe,Germany) for collecting data from the linear polarizer side. Forcomparison purposes, the measured axial luminance and integratedintensity values were set at 100% as summarized in Table II.

TABLE II Measured optical properties for Examples 1-9 Axial IntegratedHalf Brightness Example Luminance Intensity Angle (Degrees) No. (cd/m2)(lm/m2) Up Down 1 100% 100% 75 75 2 119% 121% 78 78 3 137% 138% 75 75 4131% 132% 75 75 5 128% 129% 78 78 6 130% 131% 75 75 7 126% 128% 78 78 8147% 150% 75 75 9 148% 151% 75 75

Example 2

An optical construction was made that was similar to the opticalconstruction made in Example 1, except that adhesive 2520 was acomposition that included a polydiorganosiloxane polyoxamide containingsilyloxy-containing repeat units and a tackifier (herein after referredto as silicone pressure sensitive adhesive (SPSA) for simplicity). Therefractive index of the SPSA adhesive was 1.41. The measured opticalproperties are summarized in Table III. The axial luminance andintegrated intensity values were normalized relative to thecorresponding values measured in Example 1. The axial luminance of theoptical construction in Example 2 was about 19% greater than the axialluminance of the optical construction in Example 1.

Example 3

An optical construction 2600, a side-view of which is shownschematically in FIG. 13, was made. Optical construction 2600 wassimilar to optical construction 2500, except that optical construction2600 had an optical film 2610 placed between optical adhesive layer 2520and reflective polarizer layer 430.

Volume optical diffuser 450 was made as described in Example 1. Next,coating solution A from Example A was coated on a DBEF-Q reflectivepolarizer layer 430 using the coating method described in Example Eresulting in optical film 2610 coated on reflective polarizer layer 430.The optical film had an index of refraction of about 1.28 and athickness of about 4 microns. Optical adhesive 2520 (OCA 8171 having anindex of refraction 1.48) was used to laminate the substrate side of thevolume diffuser to the optical film. SPSA optical adhesive layer 2530was used to laminate the reflective polarizer to linear absorbingpolarizer 2540, where the absorbing polarizer was similar to theabsorbing polarizer used in Example 1.

The measured optical properties of optical construction 2600 aresummarized in Table II. The axial luminance and integrated intensityvalues were normalized relative to the corresponding values measured inExample 1. The axial luminance of the optical construction in Example 3was about 37% greater than the axial luminance of the opticalconstruction in Example 1.

Example 4

An optical construction similar to Example 3 was made except that theLEDs were run at 6 Amps resulting in a UV-A dose of 0.174 joules persquare cm. Optical film 2610 had an index of refraction of about 1.32and a thickness of about 4 microns.

The measured optical properties of the optical construction aresummarized in Table II. The axial luminance and integrated intensityvalues were normalized relative to the corresponding values measured inExample 1. The axial luminance of the optical construction in Example 4was about 31% greater than the axial luminance of the opticalconstruction in Example 1.

Example 5

An optical construction similar to Example 3 except that thesyringe-pump rate was 2 cc/min. Optical film 2610 had an index ofrefraction of about 1.34 and a thickness of about 3 microns.

The measured optical properties of the optical construction aresummarized in Table II. The axial luminance and integrated intensityvalues were normalized relative to the corresponding values measured inExample 1. The axial luminance of the optical construction in Example 5was about 28% greater than the axial luminance of the opticalconstruction in Example 1.

Example 6

An optical construction similar to Example 3 was made except that adifferent optical film 2610 was made. First, 10 g of Dyneon THV 200 (afluoroplastic resin available as a 10% by weight solution in MEK fromDyneon LLC, Oakdale, Minn.) was mixed with 20 g of PTFE F-300 (apolytetrafluoroethylene non-porous low index micropowder available fromMicropowder Technologies, Tarrytown, N.Y.) in a 500 ml stainless steelbeaker. The particles in the PTFE had an average diameter of about 5-6microns, and about 95% of the particles had a diameter less than about22 microns.

Next, an additional 100 g of MEK was added and the mixture was slowlyagitated resulting in a mixture at 15% solids by weight in MEK. Theweight ratio of THV to PTFE was approximately 1:2. Next, the mixture byweight THV-PTFE coating formulation at 15% solids MEK. The PTFEmicropowder was further dispersed in the solution using a Ross 100-LCsingle stage high shear mixer (available from Charles Ross and Sons,Hauppaugne, N.Y.) that was equipped with a single stage slotted headrotor. The mixture was stirred for approximately 3 min at 1200 rpm.Next, fumed silica TS-530 (available as TS-530 from Cabot Corporation,Billerica Mass.) was added to the mixture resulting in a coatingsolution for making the optical film.

The coating solution was coated on DBEF-Q reflective polarizer using ahand-held knife coater set to a gap of about 102 microns. The wetcoating was dried at room temperature for about 5 min and than furtherdried at 65° C. for 3 minutes. The dried coating had a thickness ofabout 4 microns and an index of refraction of about 1.35.

The measured optical properties of the optical construction aresummarized in Table II. The axial luminance and integrated intensityvalues were normalized relative to the corresponding values measured inExample 1. The axial luminance of the optical construction in Example 6was about 30% greater than the axial luminance of the opticalconstruction in Example 1.

Example 7

An optical construction similar to Example 3 was made, except that adifferent optical film 2610 was made. First, a 10% by weight solution ofSPU-5K (see, Example G) in 2-propanol was prepared. Next, SPU-5K, asilicone poly urea prepared as described in U.S. Pat. No. 6,355,759,Example 23, for which a masterbatch solution of this polymer wasprepared as 10 wt % in 2-propanol. Next, fumed silica TS-530 was addedto the solution resulting in a coating solution for making the opticalfilm. The weight ration of SPU-5K to the fumed silica was about 1:5.Next, sufficient 2-propanol was added to the solution resulting in acoating solution at 12% solids by weight.

The resulting coating solution was coated on a DBEF-Q reflectivepolarizer layer 430 using a number 30 Meyer rod (available from RDSpecialties, Webster N.Y.). The resulting wet coating thickness wasapproximately of 76.2 microns. The wet coating was dried at roomtemperature for about 5 min and than further dried at 65° C. for 3 min.The dried coating had a thickness of about 2.6 microns and an index ofrefraction of about 1.25.

The measured optical properties of the optical construction aresummarized in Table II. The axial luminance and integrated intensityvalues were normalized relative to the corresponding values measured inExample 1. The axial luminance of the optical construction in Example 7was about 26% greater than the axial luminance of the opticalconstruction in Example 1.

Example 8

An optical construction 2700, a side-view of which is schematicallyshown in FIG. 14, was made. Optical construction 2700 was similar tooptical construction 2500 in FIG. 12, except that optical construction2700 had an optical construction 2730 and an optical adhesive layer 2705placed in between optical adhesive 2520 and substrate 2510. Opticalconstruction 2730 included an optical film 2710 coated on a substrate2720.

Volume optical diffuser 450 was coated on a PET substrate as describedin Example 1. Next, coating solution B from Example B was coated on a0.051 mm thick PET substrate 2720 using the coating method described inExample E except that the UV-LEDs were run at 6 Amps, resulting in aUV-A dose of 0.174 joules per square cm. The resulting optical film 2710had an index of refraction of about 1.20 and a thickness of about 5microns. Next, the PET side of the volume diffuser was laminated tooptical film 2710 using optically clear adhesive OCA 8171 (layer 2705).SPSA optical adhesive layer 2520 was used to laminate PET substrate 2720to reflective polarizer layer DBEF-Q 430. Next, SPSA optical adhesivelayer 2530 was used to laminate the reflective polarizer to linearabsorbing polarizer 2540, where the absorbing polarizer was similar tothe absorbing polarizer used in Example 1.

The measured optical properties of the optical construction aresummarized in Table II. The axial luminance and integrated intensityvalues were normalized relative to the corresponding values measured inExample 1. The axial luminance of the optical construction in Example 8was about 47% greater than the axial luminance of the opticalconstruction in Example 1.

Example 9

An optical construction similar to Example 8 was made except that theLEDs were run at 7 Amps, resulting in a UV-A dose of 0.195 joules persquare cm. Optical film 2710 had an index of refraction of about 1.19and a thickness of about 7 microns.

The measured optical properties of the optical construction aresummarized in Table II. The axial luminance and integrated intensityvalues were normalized relative to the corresponding values measured inExample 1. The axial luminance of the optical construction in Example 9was about 48% greater than the axial luminance of the opticalconstruction in Example 1.

Example 10

An optical construction 2700, a side-view of which is schematicallyshown in FIG. 14, was made. Optical construction 2700 was similar tooptical construction 2500 in FIG. 12, except that optical construction2700 had an optical construction 2730 and an optical adhesive layer 2705placed in between optical adhesive 2520 and substrate 2510. Opticalconstruction 2730 included an optical film 2710 coated on a substrate2720.

Volume optical diffuser 450 was coated on a PET substrate as describedin Example 1. Next, a coating solution from Example H was coated on a0.1275 mm thick PET substrate 2720 using a #30 wire-wound rod and driedat 100° C. for 1 min. The resulting optical film 2710 had an index ofrefraction of about 1.174, an optical haze of about 5%, and a thicknessof about 5 microns. Next, the PET side of the volume diffuser waslaminated to optical film 2710 using optically clear adhesive OCA 8171(layer 2705). SPSA optical adhesive layer 2520 was used to laminate PETsubstrate 2720 to reflective polarizer layer DBEF-Q 430. Next, SPSAoptical adhesive layer 2530 was used to laminate the reflectivepolarizer to linear absorbing polarizer 2540, where the absorbingpolarizer was similar to the absorbing polarizer used in Example 1.

The axial luminance of the optical construction in Example 10 was about43% greater than the axial luminance of the optical construction inExample 1.

Example 11

An optical construction 2700, a side-view of which is schematicallyshown in FIG. 14, was made. Optical construction 2700 was similar tooptical construction 2500 in FIG. 12, except that optical construction2700 had an optical construction 2730 and an optical adhesive layer 2705placed in between optical adhesive 2520 and substrate 2510. Opticalconstruction 2730 included an optical film 2710 coated on a substrate2720.

Volume optical diffuser 450 was coated on a PET substrate as describedin Example 1. Next, coating solution C from Example C was coated on a0.051 mm thick PET substrate 2720 using the coating method described inExample E except that that the syringe-pump rate was 10 cc/min and theLEDs were run at 10 Amps resulting in a UV-A dose of 0.249 joules persquare cm. The resulting film had an optical transmittance of about 92%transmission, an optical haze of about 5%, an optical clarity of about99.7%, and a refractive index of about 1.15. Next, the PET side of thevolume diffuser was laminated to optical film 2710 using optically clearadhesive OCA 8171 (layer 2705). SPSA optical adhesive layer 2520 wasused to laminate PET substrate 2720 to reflective polarizer layer DBEF-Q430. Next, SPSA optical adhesive layer 2530 was used to laminate thereflective polarizer to linear absorbing polarizer 2540, where theabsorbing polarizer was similar to the absorbing polarizer used inExample 1.

The axial luminance of the optical construction in Example 11 was about52% greater than the axial luminance of the optical construction inExample 1.

Example 12

Optical construction 3500, schematic side-view of which is shown in FIG.15, was made. The optical construction included an optical film 3520coated on a DBEF-Q reflecting polarizer layer (available from 3MCompany, St. Paul Minn.). The coating solution from Example D was coatedon DBEF using the coating method described in Example F except that thesyringe-pump rate was 4.5 cc/min and the current to the LEDs was 13Amps, resulting in a UV-A dose of 0.1352 joules per square cm. Theresulting optical film 3520 had a refractive index of 1.17 and athickness of about 6 microns.

Next, the PET side of the volume diffuser was laminated to optical film3520 using optically clear adhesive OCA 8171. Next, SPSA opticaladhesive layer 2530 was used to laminate the reflective polarizer tolinear absorbing polarizer 2540, where the absorbing polarizer wassimilar to the absorbing polarizer used in Example 1. The axialluminance of the optical construction in Example 12 was about 50%greater than the axial luminance of the optical construction in Example1.

Example 13

Seven optical constructions 1600, schematic side-views of which areshown in FIG. 16, were made. Each optical construction 1600 included anoptical film 1650 laminated to a DBEF-Q reflecting polarizer layer 1640(available from 3M Company, St. Paul Minn.) via a first optical adhesivelayer 1640 (available as OCA 8171 from 3M Company, St. Paul Minn. havingan index of refraction of about 1.48). The other side of polarizer layer1620 was laminated to a linear absorbing polarizer 1610 (available asSR5618 from San Ritz Corporation, Tokyo Japan) via a second opticaladhesive layer 1620 (OCA 8171). Seven different optical films 1650(labeled OF1-OF7) were selected:

-   -   Optical film 1 (OF1): An optically diffusive CELGARD 2500        available from Celanese Separation Products of Charlotte, N.C.        OF1 was a porous film with 25 micron voids and a porosity of        55%. The thickness, optical haze, optical clarity, and photopic        transmittance of sample OF1 are given in Table III.    -   Optical film 2 (OF2): A porous optically diffusive film made        according to the teachings of U.S. Pat. Nos. 5,993,954 and        6,461,724. OF2 had a pore size in a range from about 100 nm to        about 200 nm. The thickness, optical haze, optical clarity, and        photopic transmittance of sample OF2 are given in Table III.    -   Optical film 3 (OF3): A TIPS optically diffusive porous film        made according to the teachings of U.S. Pat. Nos. 4,539,256;        4,726,989; and 5,238,623 and had a plurality of interconnected        voids and a plurality of interconnected polymer filaments as        exemplified in FIG. 7. OF3 was oriented and had elongated voids        with a void diameter in a range from about 1 micron to about 2        microns. The polymer filaments had filament diameter in a range        from about 0.1 microns to about 0.2 microns. The thickness,        optical haze, optical clarity, and photopic transmittance of        sample OF3 are given in Table III.    -   Optical film 4 (OF4): A porous optically diffusive oriented        PET/polypropylene blend. The film composition was 69% PET, 30%        PP, and 1% Hytrel G4074 compatibilizer (available from DuPont        Engineering Polymers, Wilmington, Del.). The film was made on a        standard polyester film making line. The starting components        were blended in an extruder which fed a film making die. The        cast web was then sequentially oriented using standard polyester        film making process conditions. Typical pore size was in a range        from about 5 microns to about 10 microns. The thickness, optical        haze, optical clarity, and photopic transmittance of sample OF4        are given in Table III.    -   Optical film 5 (OF5): A porous PVDF film having a plurality of        interconnected voids and a plurality of interconnected polymer        filaments. The average pore size was about 12 microns. The pore        size was in a range from about 5 microns to about 30 microns.        The polymer filament diameter was in a range from about 1 micron        to about 10 microns. The thickness, optical haze, optical        clarity, and photopic transmittance of sample OF5 are given in        Table III.    -   Optical film 6 (OF6): A non-porous optically diffusive ScotchCal        3635-70 (available from 3M Company, St. Paul, Minn.). OF6 was a        vinyl film filled with TiO₂ pigment. The amount of TiO₂ pigment        in the film was adjusted so that the transmission was about 50%.        The thickness, optical haze, optical clarity, and photopic        transmittance of sample OF6 are given in Table III.    -   Optical film 7 (OF7): A non-porous optically diffuser film        having a plurality of polystyrene particles was made similar to        volume diffuser 450 in Example 1. The thickness, optical haze,        optical clarity, and photopic transmittance of sample OF7 are        given in Table III.

TABLE III Properties of optical films and constructions in Example 13Sample Thickness Optical Optical Transmit- Optical No. (microns) Haze(%) Clarity (%) tance (%) Gain (%) OF1 25 98.6 1.4 55 136 OF2 25 98.2 250 134 OF3 13 98.1 2.5 23 151 OF4 85 98.3 2.5 39 126 OF5 115 98.3 0 25133 OF6 50 98.5 2.3 50 106 OF7 39 98.5 2 45 105

The gain for each optical construction 1600 was made. First, the opticaltransmittance T_(a) of the construction was measured before laminatinglinear polarizer 1610 (that is, with an air layer between linearpolarizer 1610 and reflective polarizer layer 1630). Next, thetransmission T_(b) of the optical construction was measured after thelinear polarizer was laminated to the reflective polarizer layer usingsecond optical adhesive layer 1620. The optical gain for each sample wasthe ration T_(b)/T_(a). The optical gain values for the seven opticalconstructions 1600 are given in Table VI. Optical constructions thatincluded porous optical films 1650 (that is, OF1-OF5) had significantlyhigher optical gains than optical constructions that included non-porousoptical films (that is, OF6 and OF7). The porous optical films OF1-OF5produced higher optical gains because these films had narrowerscattering distributions inside the reflective polarizer layer ascompared to the scattering distributions of optical films OF6 and OF7.

Example 14

The coating solution from Example I was coated according to Example F ona 2 mil (0.051 mm) thick PET substrate except that the syringe flow-ratewas 6 cc/min and the current to the LEDs was at 13 Amps, resulting in aUV-A dose of 0.1352 joules per square cm. The resulting optical film hada total optical transmittance of about 52%, an optical haze of about100%, an optical clarity of about 4%, and a thickness of about 8microns.

An optical construction 3500, a schematic side-view of which is shown inFIG. 15, was made. The optical construction included an optical film3520 coated on a DBEF-Q reflecting polarizer layer (available from 3MCompany, St. Paul Minn.). The coating solution from Example I was coatedon a DBEF-Q film using the coating method described in Example F exceptthat the syringe-pump rate was 6 cc/min and the current to the LEDs wasat 13 Amps, resulting in a UV-A dose of 0.1352 joules per square cm,resulting in a high haze optical film coated on DBEF-Q.

Next, SPSA optical adhesive layer 2530 was used to laminate the otherside of the reflective polarizer to linear absorbing polarizer 2540,where the absorbing polarizer was similar to the absorbing polarizerused in Example 1. The axial luminance of the optical construction inExample 14 was about 43% greater than the axial luminance of the opticalconstruction in Example 1.

As used herein, terms such as “vertical”, “horizontal”, “above”,“below”, “left”, “right”, “upper” and “lower”, “clockwise” and “counterclockwise” and other similar terms, refer to relative positions as shownin the figures. In general, a physical embodiment can have a differentorientation, and in that case, the terms are intended to refer torelative positions modified to the actual orientation of the device. Forexample, even if optical construction 100 in FIG. 1 is flipped ascompared to the orientation in the figure, major surface 122 is stillconsidered to be a “top” major surface.

All patents, patent applications, and other publications cited above areincorporated by reference into this document as if reproduced in full.While specific examples of the invention are described in detail aboveto facilitate explanation of various aspects of the invention, it shouldbe understood that the intention is not to limit the invention to thespecifics of the examples. Rather, the intention is to cover allmodifications, embodiments, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

What is claimed is:
 1. An optical construction comprising: a reflectivepolarizer layer; and an optical film disposed on the reflectivepolarizer layer and having an optical haze that is not less than about50%, wherein substantial portions of each two neighboring major surfacesin the optical construction are in physical contact with each other, andwherein the optical construction has an axial luminance gain that is notless than about 1.2.
 2. The optical construction of claim 1, wherein thereflective polarizer layer comprises a multilayer optical filmcomprising alternating layers, wherein at least one of the alternatinglayers comprises a birefringent material.
 3. The optical construction ofclaim 1, wherein the reflective polarizer layer comprises a wire gridreflective polarizer.
 4. The optical construction of claim 1, whereinthe reflective polarizer layer comprises a cholesteric reflectivepolarizer.
 5. The optical construction of claim 1, wherein the opticalfilm has an optical haze that is not less than about 60%.
 6. The opticalconstruction of claim 1, wherein the optical film has an optical hazethat is not less than about 70%.
 7. The optical construction of claim 1,wherein the optical film has an optical haze that is not less than about80%.
 8. The optical construction of claim 1, wherein the optical filmhas an optical haze that is not less than about 90%.
 9. The opticalconstruction of claim 1, wherein the optical film has a thickness thatis not less than about 1 micron.
 10. The optical construction of claim1, wherein the optical film has a thickness that is not less than about2 microns.
 11. The optical construction of claim 1, wherein the opticalfilm comprises a plurality of voids.
 12. The optical construction ofclaim 10, wherein the plurality of voids comprises a plurality ofinterconnected voids.
 13. The optical construction of claim 1, whereinthe optical film comprises: a binder; a plurality of interconnectedvoids; and a plurality of particles, wherein a weight ratio of thebinder to the plurality of the particles is not less than about 1:2. 14.The optical construction of claim 13, wherein the plurality ofinterconnected voids has an average void size that is not greater thanabout 2 microns.
 15. The optical construction of claim 13, wherein theplurality of interconnected voids has an average void size that is notgreater than about 1 micron.
 16. The optical construction of claim 13,wherein a volume fraction of the plurality of the interconnected voidsin the optical film is not less than about 20%.
 17. The opticalconstruction of claim 13, wherein a volume fraction of the plurality ofthe interconnected voids in the optical film is not less than about 40%.18. The optical construction of claim 13, wherein the plurality ofparticles has an average size that is not greater than about 100 nm. 19.The optical construction of claim 13, wherein the plurality of particleshas an average size that is not greater than about 50 nm.
 20. Theoptical construction of claim 13, wherein the plurality of particlescomprises elongated particles.
 21. The optical construction of claim 1,wherein at least 50% of each two neighboring major surfaces of theoptical construction are in physical contact with each other.
 22. Theoptical construction of claim 1, wherein at least 70% of each twoneighboring major surfaces of the optical construction are in physicalcontact with each other.
 23. The optical construction of claim 1,wherein at least 90% of each two neighboring major surfaces of theoptical construction are in physical contact with each other.
 24. Theoptical construction of claim 1, wherein the optical film is laminatedto the reflective polarizer layer via an optical adhesive layer.
 25. Theoptical construction of claim 1, wherein the optical film is coated onthe reflective polarizer layer.
 26. The optical construction of claim 1having an axial luminance gain of no less than about 1.2.
 27. Theoptical construction of claim 1 having an axial luminance gain of noless than about 1.3.
 28. The optical construction of claim 1 having anaxial luminance gain of no less than about 1.4.
 29. The opticalconstruction of claim 1 further comprising an optical adhesive layerdisposed on the reflective polarizer layer.
 30. The optical constructionof claim 1 further comprising a liquid crystal panel disposed on thereflective polarizer layer.
 31. The optical construction of claim 1,wherein the optical film has an optical clarity that is not greater thanabout 10%.
 32. The optical construction of claim 1, wherein the opticalfilm has an optical clarity that is not greater than about 7%.
 33. Theoptical construction of claim 1, wherein the optical film has an opticalclarity that is not less than about 50%.
 34. The optical construction ofclaim 1, wherein the optical film has an optical clarity that is notless than about 70%.
 35. The optical construction of claim 1, whereinthe optical film has an optical clarity that is not less than about 80%.36. The optical construction of claim 1, wherein the optical film has anoptical clarity that is not less than about 90%.
 37. A direct-litdisplay system comprising: the optical construction of claim 1; and atleast one lamp facing the optical construction.
 38. The direct-litdisplay system of claim 37, wherein the at least one lamp is at leastpartially within a reflective optical cavity.
 39. An edge-lit displaysystem comprising: a lightguide; a lamp disposed along an edge of thelightguide; and the optical construction of claim 1 disposed on thelightguide.
 40. An optical construction comprising: a reflectivepolarizer layer; and an optical film disposed on the reflectivepolarizer layer and having a plurality of voids and an optical haze thatis not less than about 50%, wherein substantial portions of each twoneighboring major surfaces in the optical construction are in physicalcontact with each other.
 41. The optical construction of claim 40,wherein the optical film has an optical haze that is not less than about60%.
 42. The optical construction of claim 40, wherein the optical filmhas an optical haze that is not less than about 70%.
 43. The opticalconstruction of claim 40, wherein the optical film has an optical hazethat is not less than about 80%.
 44. The optical construction of claim40 having an axial luminance gain of no less than about 1.2.
 45. Theoptical construction of claim 40 having an axial luminance gain of noless than about 1.3.